Method of measuring inclining angle of planar defect of solid material by ultrasonic wave

ABSTRACT

A method of measuring the inclining angle of a planar defect of a solid material with ultrasonic waves which includes the steps of irradiating ultrasonic waves incident to the planar defect of a solid material while longitudinally scanning a probe forwardly and backwardly. The inclining angle of the planar defect is determined based on the inclination of an echo envelope obtained from the relationship of the echo beam path distances of the ultrasonic waves versus the echo amplitudes or heights of the reflected waves reflected from the planar defect of the solid material. The inclining angle of the defect corresponds to a straight line portion of the echo envelope in a region where the echo height decreased gradually from a maximum height position as the echo beam path distance increases. Measurements can be made non-destructively with one probe and the inclining angle of the planar defect generated within an element or a member forming part of an electronic or mechanical apparatus can be determined accurately in an extremely efficient manner.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method of measuring the inclining angle of aplanar defect in various solid materials by utilizing ultrasonic waves.

The planar defect in a solid material in this specification means a flatsurface-state defect and hence a planar defect having an area,generated, for example, on a part or component, or a member whichconstructs an apparatus such as an electric apparatus, a mechanicalapparatus or a chemical apparatus in various industrial fields, andinvolves the state wherein the planar defect is opened on the surface aswell as the state wherein the defect is partly opened on the surface,but the state irrespective of the length of the planar defect and themagnitude of the width of the opening. The solid material in thisinvention involves metal and nonmetal (glass, ceramics, concrete,synthetic resin, rubber and/or wood) and hence a physical body in whichultrasonic waves can be propagated.

Further, the inclining angle of the planar defect in the solid materialin this specification means the angle formed between the planar defectin the solid material and the surface or plane of the part or member inwhich the planar defect is generated.

2. Description of the Prior Art

In the technical field relating to this invention, it is a necessary andimportant matter to examine the presence or absence of a defect in apart or component, or a member of an apparatus and to know, in the casewhere the defect exists, the position, shape, type and size of thedefect. If there is a planar defect like a crack as type of the defect,in not only the part or member but also destructive dynamics andproposal of countermeasures involving the strength analysis and thelifetime calculation of the entire apparatus, it is important andindispensable to know the type of the planar defect and the incliningangle thereof. There are a number of types of planar defects such as aflat surface defect caused, for example, by improper fusion during thecourse of welding; a cleavage generated near the surface of a membercaused by the fatigue of the member, a thermal stress or atransformation stress upon quenching or tempering or remaining stressduring ambient temperature release of the member having the remainingstress; or a crack due to stress corrosion cracking or grain boundarycorrosion feasibly generated in a coating material or a heavy metalcasing of an atomic reactor fuel used in a corrosive environment or alarge-sized storage tank for LPG or gaseous fuel due to tensile stressof a material such as stainless steel or Zr-alloy steel having hightensile strength, toughness and corrosion resistance. The known methodsof non-destructively detecting the position and approximate size of aplanar defect include detecting the defects by utilizing radiationtransmission of X-rays or gamma-rays, of physical energy such aspenetration of supersonic waves, magnetic or electric induction, orimpregnation with a solution, which are used distinctly according to thetypes of defects to be detected, i.e., predetermined correlative size.However, there are no known methods of measuring the including angle ofthe planar defect at present, and the only practical method of measuringa planar defect itself being by taking a photograph of the defect.However, since the result of the test is affected by the results of thetaken photograph in this method, it is necessary to provide forselection of film sensitivity and a series of photograph forming stepsto the formation of a print, to provide for the shape and the size of anelement to be detected in a photographing state, to form a print of highresolution, as well as providing a detecting apparatus having a largescale in consideration the attenuation or scattering of radioactive rayenergy due to the material and the size of the element to be detected.In addition, there are special problems with regard to safety duringexposure of radioactive rays, thereby resulting in a number ofconditions in the measurements. Thus, most cases cannot be simply andaccurately measured. The ultrasonic wave flaw detecting method of theother above-described detecting methods offers the possibility ofmeasurements, but most disclosures involve qualitative descriptionsrelating to the size of the detect instead of the inclining angle of aplanar defect, and there is no report of measuring the inclining angleof the planar defect in fact. On the other hand, there is disclosed anexperimental report which is based on the assumption that the incliningangle is related to the measurement of the height of a welding crack (in"Non-destructive Inspection", Vol. 26, No. 5, pages 336 to 340, issuedin May, 1977). This will be described with reference to FIGS. 16 and 17.FIG. 16 is a view illustrating an experimental state, and this is amethod of experimentally measuring with two probes a crack of a planardefect produced by artificially altering a length (h), a height (h') andan inclining angle (alpha) in the butt welded portion of a steel platewith the surfaces of the steel plate at both sides of a welding line asthe surfaces to be detected by opposing oblique angle probes in contactwith the surfaces, longitudinally scanning the probes forwardly andbackwardly. In the figures, numeral 100 denotes a steel plate of anelement to be detected (material SS41: JISG 3101 by the JapaneseIndustrial Standards), one test piece having a thickness of 10.7 mm andsixteen test pieces each having a thickness of 21-24 mm are employed,three cracks 101 are produced within the width of the test piece per onetest piece, and experiments are conducted for a total of fifty-onesamples. The inclining angle alpha of the crack 101 involves four anglesof 0°, 10°, 20° and of the 51 samples 30°, and there are 21 for 0°, 6for 10°, 9 for 20° and 15 for 30°. The width of one test piece 1 is 150mm. Numerals 200 and 201 denote probes of model 2.25Z10x18 A 70 (JIS Z2344). The probes 200 and 201 are opposed in contact on the surfaces 102and 103 to be detected at both sides of the crack 101, and scannedlongitudinally with respect to the crack 101 forwardly and backwardly.The catalytic medium is machine oil. The probes 200 and 201 areconnected to a pulse reflection type ultrasonic flaw detecting apparatus(hereinbelow termed as "an ultrasonic flaw detector") of A scopedisplay, (not shown) through a high frequency cable, with the detectingsensitivity of STB-A2-φ4(1S) (JIS Z 2348) as a reference (0 dB). Themaximum echoes of the amplitudes V_(A) and V_(B) are obtained by theprobes 200 and 210 from the crack 101 in the vicinity of skips of 0.75at the probe distance (the passage of a beam x sin 70°) l of the probes200 and 201, the absolute value (ΔV) of the difference of both isobtained, and the inclining angle α of the crack 101 is obtained fromthe correlation of the absolute value ΔV and the inclining angle α ofthe crack 101. FIG. 17 is a graph illustrating the experimental results.The ordinate axis of the graph designates the difference ΔV (dB) of themaximum echo amplitudes obtained by the probes 200 and 201, and theabscissa axis designates the inclining angle α (degrees) of the defect.In the graph, a solid line denotes a line for coupling the averagevalues of the measured values in the inclining angle α, and as reported,there is described the degree, "the experimental results have largeirregularity, but the inclining angle α of the crack can be presumedapproximately from the ΔV", it is accordingly impossible to accuratelyobtain information from the graph of FIG. 17, and the graph cannot beutilized for a practical purpose.

As described above, since the conventional method of measuring theinclining angle of a planar defect has a number of problems in themeasurements, the method cannot readily and accurately measure thedefect in a short time nor measure in a real-time. In particular, themeasuring method capable of being utilized for a practical purpose byutilizing ultrasonic waves has simple measuring results to be expected,but this method is not yet developed as a practical one at present.

A primary object of this invention is to provide a method of measuringthe inclining angle of a planar defect of a solid material by ultrasonicwaves which can eliminate the problems and drawbacks of theabove-described prior art and accurately and readily measure theinclining angle of a planar defect opened mainly on the surface presenton a solid material in an extremely short time without influence of thetypes, shape, size, inclination of the planar defect and the roughnessof the defect surface as well as perform the measurement in a real-time.

Another object of this invention is to provide a method of measuring theinclining angle of a planar defect of a solid material which can measurethe defects of a large quantity of elements to be detected byautomatically detecting the defect on a manufacturing or inspectingline.

The other objects of the invention will become apparent from thefollowing description.

SUMMARY OF THE INVENTION

This invention is a method of measuring the inclining angle of a planardefect with ultrasonic waves comprising the steps of irradiatingultrasonic waves incident to the planar defect of a solid material whilelongitudinally scanning a probe forwardly and backwardly and determiningthe inclining angle of the planar defect from the inclination of an echoenvelope obtained from the beam path lengths of the ultrasonic waves andthe echo amplitude of the reflected waves reflected from the planardefect in the solid material as an evaluating index by utilizing theinclination of the echo envelope.

The feature of the invention is to utilize the properties to bedescribed in the following, i.e., the properties that the inclination ofthe echo envelope of the side obtained when the probe is scanned awayfrom the maximum echo amplitude position of the echo envelope has apredetermined correlation to the inclining angle of the planar defect inthe solid material. This will be described with reference to FIG. 1 ofan explanatory view of the principle of this invention.

In FIG. 1, numeral 1 denotes an element to be detected in which thegroove 1a of a planar defect opened on the surface is formed to thedepth of substantially 1/2 of the thickness of the element. Symbol 1bdenotes the angle of the groove 1a, symbol 1c denotes a defect detectingsurface and symbol 1d denotes the surface of the element of the groove1a side. Symbol α denotes the inclining angle formed between the groove1a and the surface 1d of the element to be detected. Numeral 2 denotesan inclining angle detecting probe (hereinbelow termed as "an angle beamprobe"), which is contacted with the surface 1c to irradiate ultrasonicwaves (transversal waves) while longitudinally scanning the angle 1b ofthe groove 1a in a direction of an arrow A or B forwardly andbackwardly. Symbols 2a, 2b and 2c denote the probe located at arbitrarypositions when the probe 2 is longitudinally scanned forwardly andbackwardly. An incident ultrasonic wave 3 which arrives at the angle 1bis reflected from the angle 1b as a reflecting sound source to become areflecting wave 4, and is received by the probe 2. When the receivedreflected wave 4 is displayed on a cathode ray tube (CRT) of A scopedisplay of orthogonal coordinates having the echo amplitude h (dB) inthe ordinate axis and the echo beam path distance x (mm) in the abscissaaxis at the positions where the probe 2 is longitudinally scannedforwardly and backwardly, there is obtained an echo pattern as shown inFIG. 2. More particularly, a transmitted pulse T is displayed at theposition of an origin O on the time base of the CRT, and the echoes ofthe reflected wave 4 (F, F_(a), F_(b), F_(c) in the drawing) aresequentially displayed at the positions corresponding to the positionslongitudinally scanned forwardly and backwardly from the position of thetransmitted pulse T, i.e., the positions corresponding to the pathdistance x (x, x_(a), x_(b) and x_(c) in the drawing) from the incidentpoint to the angles 1b on the surface 1c to be detected by theultrasonic wave. The echo amplitudes depend upon the distances x of thebeams at the positions of the probe 2, and when the vertexes of therespective echo amplitudes (h) of the ordinate axis with respect to thedistances (x) of the beams of the abscissa axis at the positions of theprobe 2 are coupled by a line, an echo envelope 5 having a vertex at themaximum echo amplitude F is obtained. If the groove 1a is not presentedin this case, the reflected wave 4 is not generated, and no echoenvelope 5 is obtained. The shape of the echo envelope 5 is determinedaccording to the echo amplitude (h) of sound pressure decided by theproduct of (the directivity of transmitted wave determined by thevibrator size and the frequency of the probe 2), (the reflectingdirectivity of the case where the ultrasonic wave is reflected from thegroove (planar defect) 1a determined by the position, shape, size,surface roughness and inclining angle of the groove (planar defect) 1a)and (the directivity of the case where the reflected wave 4 is fedthrough the scattering and the attenuation including the diffraction ofthe ultrasonic wave). Thus, when the same planar defect is detected withthe same probe, the directivity of the vibrator and hence transmittedand received waves is constant, the shape of the echo envelope thusobtained is also constant, and the shape of the envelope is determinedonly by the reflecting directivity varying with respect to the positionand the inclining angle of the planar defect. In the case as shown inthe drawings, the position, shape and size of the groove (planar defect)1a are as described above, and the surface roughness is approx. 20micron of average roughness, and the inclining angle α for the echoenvelope 5 shown is 90°. When the inclining angle α of the groove 1a asshown is gradually varied from 90° at small angles toward an acute angleside and the probe 2 is longitudinally scanned forwardly and backwardly,the shape of the echo envelope 5 thus obtained gradually becomes morenarrow in the reflecting directivity at the maximum echo amplitude F asa center, the inclination of the echo envelope 5 obtained when scannedto the side that the distance x of the beam is increased in length fromthe position of the maximum echo amplitude F, i.e., the side thatscanned to the direction of an arrow B becomes abrupt, and the envelopehas the inclination of a substantially rectilinear line as shown by theone-dotted chain line 6 in FIG. 1. The method of determining theinclining angle of the planar defect of this invention is to measure theinclining angle of the planar defect by utilizing a predeterminedcorrelation which exists between the inclining angle of the planardefect and the inclination of the linear line of the echo envelope ofthe side on which the distance of the beam becomes longer from themaximum echo amplitude position of the echo envelopes. Since the echoenvelope can be readily obtained from the echo amplitude of thereflected wave displayed on the CRT in response to the variousproperties of the planar defect including the inclining angle, thecorrelation to the inclining angle of the planar defect can besimultaneously obtained readily. Therefore, in comparison with theconventional method of obtaining the inclining angle from the differenceof the maximum echo amplitudes with two probes from both sides of theplanar defect, the method of this invention can accurately measure theinclining angle of the planar defect opened on the surface of a membermainly of an element to be detected by longitudinally scanning one probeforwardly and backwardly in an extremely short time in a real-timewithout limit in the properties of the planar defect. This feature ofthe invention can readily measure a large quantity of elements to bedetected by automatically detecting the planar defects.

The foregoing description has been with respect to the planar defectopened on the surface of the element to be detected. The properties ofthe feature of the invention can be also utilized for planar defect notopened on the surface of the element to be detected, though partly undercertain conditions. More specifically, the condition is that the nearestdistance from the surface of a member to the planar defect is approx.1/2 or less of the wavelength of the frequency of the used probe. Sincethe planar defect under this condition has a small gap of approx. 1 mmbetween the planar defect and the surface of the member as a reflectingsound source similar to the angle 1b in FIG. 1, the incident ultrasonicwave is reflected similarly to the angle 1b from the sound source.Therefore, the echo envelope can be obtained by the same method as inthe case of the opened defect, and the inclining angle of the planardefect not opened on the surface can be measured similarly to the caseof the opened defect.

The correlation between the inclination of the above-described echoenvelope and the inclining angle of the planar defect will be describedin more detail as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view of a principle of a method of measuring aplanar defect according to this invention, and

FIG. 2 is an explanatory view showing an echo pattern on a CRT obtainedby the method illustrated in FIG. 1.

FIGS. 3 to 12 are explanatory views a first embodiment of thisinvention, wherein

FIG. 3 is an explanatory view of the general characteristics thereof,

FIG. 4 is a side view of an element to be detected and used in theembodiment of FIG. 3, and

FIG. 5 is a view as seen from arrows V--V of FIG. 4.

FIG. 6 is an explanatory view of scanning an element to be detectedhaving a 10° inclining angle of a planar defect in the element to bedetected in FIG. 4, and

FIG. 7 is a graph illustrating an envelope obtained from therelationship between the distance of the beam and the echo amplitude bythe method shown in FIG. 6.

FIG. 8 is an explanatory view of scanning an element to be detectedhaving a 45° inclining angle of a planar defect, and

FIG. 9 is a graph illustrating an envelope obtained by a method shown inFIG. 8.

FIG. 10 is an explanatory view of scanning an element to be detectedhaving a 90° inclining angle of a planar defect, and

FIG. 11 is a graph illustrating the envelope obtained by a method shownin FIG. 10.

FIG. 12 is a graph illustrating the correlation between the incliningangle (a) of a planar defect formed in an element to be detected asshown in FIG. 4 and the proportional constant showing the inclination ofthe envelope of a returning formula obtained by the method in FIG. 3.

FIGS. 13 to 15 are explanatory views of a second embodiment according tothis invention, wherein

FIG. 13(a) is a side view of an element to be detected in the case wherethe inclining angle of a planar defect used for the embodiment is 10°,

FIG. 13(b) is a view of the case where the inclining angle is 45°,

FIG. 13(c) is a view of the case where the inclining angle is 90°,

FIG. 14 is a detailed view of the portion "C" of FIG. 13(a), and

FIG. 15 is a graph for explaining the measuring error of the incliningangle measured according to this invention.

FIG. 16 is a view illustrating the experimental states of two probes formeasuring the inclining angle of a crack with respect to the measurementof the amplitude of a welding crack by a conventional defect detectingmethod, and

FIG. 17 is a graph showing the experimental results obtained by theexperiments shown in FIG. 16.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the present invention will be described in detailwith reference to FIGS. 3 to 12. In the drawings, the same referencenumerals and symbols as those in FIGS. 1 and 2 denote the same orequivalent elements and members.

In FIG. 3, a probe 2 is connected to an ultrasonic defect detector 7through a high frequency cable. When the probe 2 is longitudinallyscanned forwardly and backwardly on a defect detecting surface 1c in adirection of an arrow A or B with respect to the edge 1b of a groove 1a,an incident ultrasonic wave 3 is reflected at the edge 1b as areflecting sound source, and displayed together with a transmitted pulseT at positions corresponding to the distance of the beam of the incidentultrasonic wave 3 on a CRT as the echo F of the reflected wave 4. Theprobe 2 used irradiates 2.25 MHz of frequency at 2.25Z10×18A70 (JISZ-2344) of refractive index of 70° with a vibrator of 10 mm×18 mm insize. The shape and the side of elements 1 to be detected and used inthe method of this embodiment are shown in FIGS. 4 and 5. A steel plate(having SS41 JIS G 3101) 14 mm (thick), 200 mm (length)×50 mm (width) isused, and a planar defect 1a having a depth 7 mm to 40 mm and a width xof 1/2 of 0.5 mm is formed at a position slightly near a surface 1dopposite to the defect detecting surface 1c. The inclining angles α ofthe planar defect 1a fall within eight types which include 10°, 15°,22.5°, 30°, 45°, 60°, 80° and 90°. The machining accuracy of theportions is approx. 20 microns (μm) (JIS B 0601) of average roughness ofthe defect detecting surface 1c, the surface 1d and the planar defect1a, and the others are similarly approx. 35 micron to 100 micron. Theresults measured by the method shown in FIG. 3 for inclining angles α of10°, 45° and 90° (which comprise three of eight types of the incliningα) are shown in FIGS. 6 to 11.

FIG. 6 shows a view of the measuring procedure in the case where theinclining angle α is 10°. When the echo amplitude h of the reflectedwave 4 of the various distances x of the beam of the incident supersonicwave 3 is plotted, a graph in FIG. 7 illustrating the echo envelope isobtained. Similarly, FIG. 8 is a view of the measuring procedure in thecase where the inclining angle is 45°, and FIG. 9 is a graphillustrating the echo envelope obtained by the measurement. FIG. 10 is aview of the measuring procedure in the case where the inclining angle αis 90°, and FIG. 11 is a graph illustrating the echo envelope obtainedby the measurement. In the graphs showing the echo envelopes of FIGS. 7,9 and 11, the abscissa axes indicate logarithmic values of the distancex (unit: mm) of the beam, and the ordinate axes indicate the maximumvalue of the echo amplitude h of reference sensitivity (0 dB), wherein"o" illustrates the measured value. Then, when returning formulae areseparately obtained at each inclining angle α by the minimum squaringmethod in a measuring range wherein the probe 2 is scanned in adirection of an arrow B away from the planar defect from the maximumecho amplitude (0 dB) of a graph showing the echo envelopes, theformulae are as listed in the following table.

    ______________________________________                                        Inclining angleα                                                                         Returning formulae                                           ______________________________________                                        10°       h = -224.9 log x + 370.9                                     45°       h = -67.9 log x + 104.3                                      90°       h = -40.0 log x + 66.0                                       ______________________________________                                    

The returning formulae in the above table become linear lines shown bysolid lines in the drawings, and the echo beam height or amplitude h canbe arranged in a simple formula as below irrespective of the incliningangle α.

    h=-a log x+b                                               (1)

where

a=proportional constant (indicating the inclination of the returningformula)

b=constant (the value of the returning formula in the above table is thevalue of the echo amplitude h in the case where the distance of beamx=1)

x=the echo beam path distanct (Unit: mm)

When the returning formulae in the above table are compared, the smallerthe values of the proportional constants "a" showing the inclination ofthe returning formula are, the larger the inclining angle α becomes.This demonstrates that the inclination of the returning formula islarge. This is clearly shown in the drawings. When the remainingelements to be detected (the remaining five types of inclining angles)are measured similarly to the above three types to obtain the returningformulae and the relationship between the proportional constants "a" ofthe respective returning formulae and the inclining angles α of theplanar defects is summarized, FIG. 12 is obtained. In the drawing, theabscissa axis indicates the logarithmic value of the inclining angle α(Unit: degree), and the ordinate axis indicates the logarithmic value ofthe proportional constant "a". In the drawing, the mark "o" denotes thevalues of the proportional constant "a" of the returning formulaeplotted. When the marks "o" are coupled, one linear line is obtainedshowing that both have excellent linear correlation. The more theinclining angle of the planar defect increases, the less the value ofthe proportional constant "a" decreases. When the returning formulae ofthe graph is obtained by the minimum squaring method, the followingformula is obtained.

    a=1381.6α.sup.-0.79                                  (2)

The above formula (2) can be modified to the following formula: ##EQU1##As understood from the formula (3), the inclining angle of the planardefect can be readily obtained if the value of the proportional constant"a" of the returning formula is obtained. When the echo envelopeobtained from the echo amplitude of the reflected wave of the variouspassages of the beam of the incident ultrasonic wave is obtained asdescribed above, the value of the proportional constant "a" of thereturning formula can be obtained from the inclination of the echoenvelope of the side in the direction for separating the probe from themaximum echo amplitude position of the echo envelope from the planardefect, i.e., obtained by scanning the probe away from the planardefect.

As understood from the description of this embodiment, the method ofmeasuring according to the invention is conducted by reflecting theincident ultrasonic wave irradiated from the probe at the angle of thegroove of the planar defect mainly as a reflecting sound source anddisplaying the echo on the CRT. Since the angle of the groove representsthe angle of the planar defect, the method of the invention can beapplied not only as to a planar defect as in this embodiment, but alsoto the measurement of the angle of the element or member which does notneed the severe preciseness like the measurement of the groove angle ofwelding.

The above-described first embodiment has been described in the casewhere a planar defect of high machining accuracy was artificially formedin the element to be detected. Now, a second embodiment of the measuringmethod of the invention applied to a planar defect generated due to awelding improper fusion of the groove will be described in detail withreference to FIGS. 13(a) to 13(c) to 15.

Elements to be detected and used in this second embodiment are shown inFIGS. 13(a) to 13(c) and 14. A total of 24 elements 1 are prepared, anda member 1A having dimensions of 14 mm (thickness)×150 mm (length)×50 mm(width) and a member 1B having the same thickness and width as themember 1A but a length of 50 mm are to be connected through a groove insuch a manner that the inclining angle of a planar defect becomes thesame as the first embodiment by butt welding. The material is the sameas the SS41 and the probe used is the same as the 2.225Z10×18A70 of thefirst embodiment. The planar defect generated due to the improper fusionof the groove is measured according to the method of this invention,then cut and actually measured. The results exhibit all the planardefects opened on the surface with the length H of the defect (thedefect amplitude when the inclining angle α is 90°) being 1.3 to 7 mm.The inclining angles α are 3 out of eight possible types of 10°, 15°,22.5°, 30°, 45°, 60°, 80° and 90°, and substantially the same types asthose of the first embodiment are obtained. The states of the planardefects of the cases are shown for the inclining angle α=10° in FIG.13(a), for the inclining angle α=45° in FIG. 13(b) and for the incliningangle α=90° in FIG. 13(c). FIG. 14 shows the detail of the portion "C"in FIG. 13(a), and the defect surfaces exhibit roughness on the grooveor fusion-bonded metal surface of the elements to be detected as shown,and the width of the defect is 0.1 to 0.2 mm. The above-mentionedelements are measured by the same method as in the first embodiment andthe results are summarized in FIG. 15. In the graph, the abscissa axisindicates the values of the intrinsic inclining angles α_(R) (Unit:degree) actually measured by cutting the elements, and the ordinate axisindicates the inclining angle α_(U) (Unit: degree) measured by themethod of this invention. The measured values are denoted by solid mark" ". In the drawings, when the measured value of the element of approx.10° of the inclining angle α is, for example, observed, the incliningangles α_(R) of the actually measured value of the three elements bycutting the element are all approx. 10°, but the inclining anglemeasured according to the method of the invention are approx. 8°, 9° and12°. In the element of approx. 45° of the inclining angle α_(R), theinclining angles α_(U) are 41°, 44°, 48.5° and in the element of approx.90°, the inclining angles α_(R) are 86°, 87.5° and 91°. When the averagevalue (x) and the standard deviation (σ) of the measuring error (α_(U)-α_(R)) are obtained for all the measured values, the following valuesare obtained.

    x=+0.08°

    σ=2.37°

The measured values are all concentrated to extremely near the linearline in the drawing of 45° of an ideal value (α_(R) =α_(U)), containedwith large margins within the range of (x±2σ=4.82°) as designated by abroken line in parallel with the linear line to thereby prove theexcellent accuracy of the measurement according to the method of theinvention. In the embodiments described above, the length H of thedefect is distributed to a range of 1.3 mm to 7 mm as described above,and accurately measured values can be obtained without influence of thelength of the length H of the detect. This is presumed from the reasonthat, if the inclining angles α of the planar defects are equal, theecho amplitude h on the CRT increases or decreases according to thelength of the length H of the defect so that the dB values of theobtained envelopes are different but the inclinations of the envelopesof the side for scanning from behind the postion of the maximum echoamplitude are all equal. The fact that the measured inclining angle ofthe planar defect is not affected by the influence of the length H ofthe defect exhibits the possibility that the small angle of a smalldefect which cannot be measured by an ordinary angle measuringinstrument can be measured. On the other hand, the defect surface isordinarily rough similarly to this embodiment such as sawtooth shape ofirregular heights, folded or bent surface, or composite surface of them.The fact that the accurately measured values are obtained in theembodiments described above also demonstrates that the defect surfacehaving the complicated inclination of the sawtooth state, folded andbent surfaces can be measured to produce the envelope on the CRT withthe average inclination of them, and when the inclination of theenvelope is calculated, the measured inclining angle of the defectsurface can be obtained without influence of the surface roughness. Thiscan be generally applied to the measurements of the opened crack oropened defect in the bead stopping end of welding due to theabove-described stress corrosion crack or Hertz stress generated overthe depth of 0.1 mm to several mm from the surface.

The proportional constant "a" and the constant "b" of the formula (1)are determined by the acoustic characteristic of the material of theelement to be detected, and when the solid materials of variousmaterials are obtained by experiments, the inclining angles of theplanar defects can be accurately measured extremely simply and readilyin the same manner as the first and second embodiments described above.

The method described above relates to a method of measuring visually bydisplaying the echo or the reflected wave on the CRT. However, it isalso possible to represent the values of analog values of the echoamplitude and the distance of the beam together with inclining angleswithout displaying them on the CRT by digitizing the analog values ofthe echo amplitude and the passage of the beam by the means ordinarilyused by those skilled in the art in this field and further calculatingthe analog amount in a relation formula correlative to the incliningangle of the planar defect to numerically express the values togetherwith the inclining angle. Further, it is also possible to diagnose adefect in a piece of equipment and preventively diagnose it or toautomatically measure a large quantity of elements to be detected in amanufacturing line by storing the numeric values in a memory andcomparing them with a reference value or threshold value.

This invention is not limited to the particular embodiments describedabove. Various other changes and modifications may be made within thespirit and scope of the present invention.

What is claimed is:
 1. A method of measuring an angle of a planar defectwithin a plate-like solid material with ultrasonic waves wherein saiddefect opens or substantially opens at a location of a first surface ofsaid solid material with an angle of up to 90 degrees with respect tosaid first surface, and wherein an angle beam probe is applied on asecond surface opposite to the first surface of the solid material, andultrasonic wave beam pulses are transmitted into the solid materialwhile said angle beam probe is traversed along said second surface in adirection towards and away from the planar defect, said traversing beingcarried out at least within a region where said beam is incident to andirradiates said location at which said defect opens or substantiallyopens comprising the steps of:receiving with said probe each reflectedwave which is reflected mainly from said location of the planar defectcorresponding to each beam path; detecting each echo height of eachreflected wave; obtaining a polygonal line forming an echo envelope inan orthogonal coordinate system defined by the echo heights and thelogarithmic values of the each beam path distances and obtaining aninclination of a portion of the echo envelope corresponding to asubstantially straight line in a region wherein the echo heightdecreases gradually from a maximum height position as the echo beam pathdistance increases; and determining the angle of the planar defect bycomparing the obtained inclination of the straight line portion of theecho envelope and predetermined reference inclinations of the planardefect.
 2. A method of measuring an angle of a planar defect within aplate-like solid material to be tested with ultrasonic waves whereinsaid defect opens at a location of a first surface of said solidmaterial with an angle of up to 90 degrees with respect to said firstsurface and wherein an angle beam probe is applied on a second surfaceopposite to the first surface of the solid material and ultrasonic wavebeam pulses are transmitted into the solid material while said anglebeam probe is traversed along said second surface in a direction towardsand away from the planar defect, said traversing being carried out atleast within a region where said beam is incident to and irradiates saidlocation at which said defect opens comprising the steps of:preparing aplurality of plate-like samples of said solid material havingartificially introduced defects with different angles with respect tosaid first surface; moving the angle beam probe over the second surfaceof each of the samples and receiving with said probe each reflected wavewhich is reflected mainly from said location of each of the artificiallyintroduced planar defects corresponding to each beam path; detectingeach echo height of each reflected wave; obtaining a polygonal lineforming an echo envelope in an orthogonal coordinate system defined bythe echo heights and the logarithmic values of the echo beam pathdistances and obtaining an inclination of a portion of the echo envelopecorresponding to a substantially straight line in a region wherein theecho height decreases gradually from a maximum height position as theecho beam path distance increases for each of the samples; determiningreturning formulas for the respective angles of the artificiallyintroduced planar defects based on the obtained inclination of thestraight line portion of each of the echo envelopes to obtainpredetermined reference inclinations of the artificially introducedplanar defects; moving said angle beam probe along said second surfaceof said material to be tested in a direction towards and away from theplanar defect therein said traversing being carried out at least withina region where said beam is incident to and irradiates said location atwhich said defect opens; receiving with said probe each reflected wavewhich is reflected mainly from said location of the planar defect in thematerial to be tested corresponding to each beam path; detecting eachecho height of each reflected wave in the material to be tested;obtaining a polygonal line forming an echo envelope in an orthogonalcoordinate system defined by the echo heights detected for the materialto be tested and the logarithmic values of the echo beam path distancesand obtaining an inclination of a portion of the echo envelopecorresponding to a substantially straight line in a region wherein theecho height decreases gradually from a maximum height position as theecho beam path distance increases; and determining the angle of theplanar defect by comparing the obtained inclination of the straight lineportion of the echo envelope for the material to be tested with saidpredetermined reference inclinations of the artificially introducedplanar defects.
 3. A method of measuring an angle of a planar defectwithin a plate-like solid material by means of ultrasonic waves whereinsaid defect is located adjacent a first surface of said material andforms an angle of up to 90 degrees therewith, comprising:predeterminedreference inclinations of portions of reference echo envelopes, each ofwhich corresponds to a substantially straight line in a region whereinecho heights decrease gradually from a maximum height position as anecho beam path distance increases, said echo envelopes beingrespectively obtained by moving an angle beam probe along secondsurfaces of samples of said material having artificially introducedplanar defects therein at different angles with respect to firstsurfaces of the samples opposite to said second surfaces, said anglebeam probe transmitting ultrasonic wave beam pulses into said samplessuch that said beam is incident to said planar defects and receivingreflected waves reflected from said planar defects, said echo envelopesbeing generated by a plot of echo heights of said reflected waves versusecho beam path distances corresponding to different positions of saidangle beam probe along said second surfaces; measuring an angle of aplanar defect within a plate-like solid material other than said samplesby means of said ultrasonic waves wherein said defect is locatedadjacent a first surface of said material and forms an angle of up to 90degrees therewith by comparing an inclination of a portion of anon-reference echo envelope to said predetermind reference inclinationsof portions of said reference echo envelopes, said inclination of saidportion of said non-reference echo envelope corresponding to asubstantially straight line in a region wherein echo heights decreasegradually from a maximum height position as an echo beam path distanceincreases, said non-reference echo envelope being obtained by moving anangle beam probe along a second surface of said material having saiddefect therein at an angle with respect to a first surface opposite tosaid second surface, said angle beam probe transmitting ultrasonic wavebeam pulses into said material such that said beam is incident to saiddefect and receiving reflected waves reflected from defect, said echoenvelope being generated by a plot of echo heights of said reflectedwaves versus echo beam path distances corresponding to differentpositions of said angle beam probe along said second surface.
 4. Themethod of claim 3, wherein said angle beam probe is moved toward andaway from said defect during said moving step.
 5. The method of claim 3,wherein said plot of echo heights of reflected waves versus echo beampath distances comprises logarithmic values on both axes of said plot.6. The method of claim 3, further comprising a step of developingreturning formulae, each of which corresponds to one of said angles ofsaid artificially introduced defects, said returning formulae beingrepresented by the formula: h=-a log x+b, wherein "a" is a proportionalconstant indicating an angle of respective one of said returningformulae corresponds to, b is a constant, x is the echo beam pathdistance, and h is the height of the echo beam.
 7. The method of claim6, where lower valves of "a" correspond to higher values of of the angleof the defect.